This invention relates to a method of separating sesamin and episesamin.
Sesame seeds contain about 0.3-0.5 weight % of d-sesamin. Unrefined sesame seed oil obtained by squeezing sesame seeds contains about 0.5-1.0 weight % of d-sesamin. If such unrefined sesame seed oil is processed with activated clay or the like, not only d-sesamin but also episesamin which is generated by optical isomerization of d-sesamin come to be contained.
It has long been known that sesamin and episesamin have strong cooperative effects on pyrethrin-type insecticides. More recently, it was reported (ISF-JOCS World Congress, (1988)) that linear polyunsaturated fatty acids such as arachidonic acid (cis-5, 8, 11, 14-eicosatetraenoic acid) and cis-5, 8, 11, 14, 17-eicosapentaenoic acid can be synthesized enzymatically in the presence of fungi (hyphomycetes). It was also reported (JAOCS 66, 237-241, (1989)) that the presence of sesamin and episesamin adversely affects the production of arachidonic acid in a production process by using fungi, while there results an accumulation of a significant quantity of dihomo-.gamma.-linolenic acid (cis-8, 11, 14-eicosatrienoic acid) which is a precursor of arachidonic acid and is considered to be difficult to synthesize enzymatically. It is now understood that this is due to the so-called enzyme inactivation effect of sesamin and episesamin, that is, the peculiar inhibitive effect of sesamin and episesamin on enzymatic dehydrogenation reaction by which arachidonic acid is generated from dihomo-.gamma.-linolenic acid. Eicosapolyenoic acids such as dihomo-.gamma.-linolenic acid and arachidonic acid are precursors of prostaglandins, thromboxanes, leucotriens, etc. which are all important biological regulators.
It is therefore an object of the present invention to provide a method of efficiently separating from sesame oil sesamin and episesamin which exhibit strong cooperative effects as mentioned above and participate in the biosynthesis of biological regulators.
Many methods of using various organic solvents to directly extract sesamin and episesamin from sesame seed oil have been attempted, including a method of using methanol as organic solvent/water (U.S. Pat. No. 2,467,903), a method of using acetone/water (U.S. Pat. No. 2,467,904), a method of using cooled petroleum ether (U.S. Pat. No. 2,557,956), a method of using acetonitrile (U.S. Pat. No. 2,786,063), and a method of using .gamma.-butylolactone (U.S. Pat. No. 2,837,534). These prior art methods, however, have the following disadvantages: (1) since the obtained extract contains a significant amount of sesamolin and glyceride in addition to sesamin and episesamin, the concentration of sesamin and episesamin in the extract is low; (2) since the concentration of sesamin and episesamin in sesame seed oil is at most about 1 weight %, a large amount of solvent must be used; (3) the cost of energy becomes quite high for distilling away the organic solvent which has been used; and (4) since organic solvents cannot be completely removed from sesame seed oil, the processed sesame seed oil, if such an organic solvent has been used, cannot serve any longer as food for hygienical reasons.
Besides the above, there has also been proposed a method of using an organic solvent for direct extraction of sesamin and episesamin from sesame seed oil and thereafter repeating recrystallization processes with the extracted liquid to refine and separate sesamin and episesamin (JAOCS, 31, 302 (1954)). This method overcomes the first of the four aforementioned disadvantages but the rest of the problems remain unsolved.
Still another method has been proposed (JAOCS 33, 197 (1956)) according to which sesamin and episesamin are directly extracted from sesame seed oil by using a molecular distillation apparatus. An apparatus for molecular distillation, however, involves a high installation cost and consumes a large amount of energy. Since sesame seed oil containing at most only about 1 weight % of sesamin and episesamin is directly fed to such an apparatus, the cost per unit amount of sesamin and episesamin obtained turns out to be extremely high. Moreover, if such sesame seed oil is directly fed into such an apparatus and is subjected to high temperatures for a long period of time, it produces conspicuously rancid flavored substances due to thermal decomposition of unsaturated glycerides which are contained or thermal polymerization of unsaturated fats. As a result, the sesame seed oil, after undergoing such a process, cannot serve as food any longer.